1. Field of the Invention
The present invention relates to radiation detection and to digital radiation imaging where the detected radiation energy is in excess of 5 keV and typically in the range 5 keV-1 MeV. In particular, the invention relates to a method of connecting a high voltage or a biasing voltage to the surface of a compound semiconductor radiation detector.
2. Description of Related Art
A semiconductor radiation detector requires a high/bias voltage on one of its surfaces to produce an electric field inside the semiconductor detector crystal. The electric field is necessary to ensure effective collection of the signal charge (electrons and holes) created in the crystal by incident radiation (X- or gamma rays or particle radiation). Conventionally the high voltage contact is provided with a thin aluminum wire with a thickness of typically 10-25 μm. The wire is generally attached by ultrasonic bonding. Other means of providing the high voltage connection between the detector surface and the Al wire include conductive epoxy or a metal spring which is brought into contact with the detector surface by mechanical pressure. These conventional means of contacting the high voltage work well in certain applications and for certain types of semiconductor detectors.
In applications where the incident radiation enters the detector crystal from the low voltage (ground/signal) side, the high voltage can be connected by means of conductive epoxy which provides electrical contact between the detector surface and the supporting substrate such as a printed circuit board (PCB). A thin aluminum wire is perfectly suitable as a high voltage connector for detectors made of silicon which is a highly mature semiconductor of well defined and stable properties.
In applications which require the high/bias voltage surface of the detector to remain bare in order to freely receive radiation, any conventional metal springs or similar means which covers all or part of the detector surface cannot be used to connect the detector high voltage. Likewise in such applications the high voltage surface cannot be glued with epoxy to a substrate. Instead, a thin wire which covers only a very small spot of the detector high voltage surface is preferred.
An example of an application requiring the detector high/bias voltage surface to remain bare is radiation imaging with hybrid detectors consisting of a semiconductor crystal (i.e., detector) bump bonded to an integrated readout circuit.